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Soluble inorganic pyrophosphatase is a ubiquitous enzyme that plays an important role in energy metabolism. Energy metabolism is made possible by soluble inorganic pyrophosphatases (PPases) by their hydrolyzing inorganic phosphates into two molecules of orthophosphate. PPases may have had an important role in evolution by aiding in accurate DNA copying during chromosome duplication. Escherichia coli (E-coli bacteria) and Saccharomyces cerevisiae (S. cerevisiae yeast) PPases, E-PPase and Y-PPase respectively, are the two best studied PPases.

Structure
E-PPase, a homohexameric protein, contains 175 amino-acid residues in each subunit. The protein's topology is described as a five stranded β-barrel that is distorted, highly twisted, and composted of strands β1, β4, β5, β6 and β7, capped on top with α-helix B and the bottom by a loop between strand five and strand six. The active site exists in the bowl formed by the excursions.

Function
PPases act to cleave PPi as it is a byproduct in many biosynthetic reactions that include protein, RNA and DNA synthesis. By cleaving the PPi in these synthesis reactions it shifts the equilibrium constants towards biosynthesis. In order to achieve PPi cleavage PPases require a divalent metal ion, usually magnesium. Calcium, alternatively, has been shown to fully suppress PPase activity. PPi hydrolysis is a complicated process that is still not fully understood.